Manufacture of envelopes having glass windows, such as the envelopes for cathode-raytubes or the like



H. E. HOLMAN ETAL- l 2,518,690 ENVELOPES HAVING GLASS WINDOWS, SUCH -RAY TUBES OR THE LIKE Filed June 25, 1948 e C T a e,

A TTORNEY INVENTQRS: n'berf Edwcvrd Holman Ra/hRe' ar%-W Aug. 15, 1950 MANUFACTURE OF AS THE ENVELOPES FOR CATHODE Patented Aug. 15, 1950 GLASS WINDOWS, SUCH AS THE ENVE- LOPES FOR CATHODE-RAY TUBES OR THE LIKE Herbert Edward Holman, West Drayton, and Ralph Reginald Pearce, Hampton, England, assignors to Electric-8r Musical Industries Limited, Hayes, England Britain a company of Great.

- Application me .25, 1948, Serial No. 35,266

In Great Britain July'2, 1947 10 Claims.

- This-invention relates to the manufacture of envelopes having glass windows, and-it relates especially, but not exclusively, to the manufacture of envelopes for cathode ray tubes suitable for use in television receivers of the projection type.

Incathode ray tubes such as are used in television receivers the end wall of the tube envelope, usually comprises the window of the tube, and it"isusual to form said wall so as to conform to a surface of'revolution generated by a curve of relatively large radius, this curvature being employed in order to obtain an envelope which is capable of: withstanding the pressure to which it is subie eted when it has been exhausted. If the tube is tobe employed in a television receiver of the projection'type, wherein an optical system is provided for projecting the image formed at the window of the-cathode ray tube on to a screen, it is also necessary for the end wall tohave a high degree. of optical'accuracyon both surfaces since it forms part of 'said optical system of the receiver, and it has been proposed toproduce said end wall separately with the desired shape and accuracy and to fuse it subsequently to the remainder-pf .the. envelope. This method, however, has the :disadvantage that the heat required to effect the fusion-frequentlycauses the curvature of said wall to lee-distorted.

Simi-Iardifficulties may arise in the manuface tore of'other pressure-tight envelopes which are required to have accurately shaped windows, and theob ject of the present invention is to provide an improved method for manufacturing envelopes having glass windows, with a view to obtaining a higher-degree of'optical accuracy in the window than hitherto. Inaccordance with the present invention there is provided a method of manufacturing an en velope comprising a glass window of predetermined shape fused to a surrounding portion of the envelope, wherein said window is formed by a glass portion which is fused to said surrounding portion and is subsequently pressed to saidpredeterminedshape. i r l In accordance with one form-of the present in-. vention there is provided a method of manufactuning the envelope of a cathoderay tube suitable for use in a television receiver of the projection type, and comprising a wall of predetermined curvature which forms the window of said envee lope, wherein said wall is formed by a glass portion which is fused to the surrounding portio oi the' envelope and is subsequently pressed to the said-predetermined curvature. 1

In order that the said invention may be clearly 2 understood and readily carried into effect, it will. now be more fully'described with reference to the accompanying drawings, in which: Y

Figure 1 illustrates a method of manufacturing glass envelopes in accordance with one exampleof the invention,

Figure 2 illustrates a modification. of this. method, and

Figure 3 illustrates a further modification. The drawings illustrate the manufacture of the envelope of a cathode ray tube intended for use in a television receiver of the projection type. The envelope of the tube is first formed, with its end wall I, which forms the window of the tube, comprising a fiat glass portion which is fused at its periphery to the bulb portion 2 of the envelope in a pressure tight manner, the bulb 2 and the neck 3 of the tube being of glass and being formed in any conventional manner. The end wall I is preferably ground and polished so that both surfaces are highly polished and accurately parallel before said wall is fused in position, care being taken during the fusing operation that the plane of the Wall is at right angles to the axis of the envelope. The envelope is then clamped with its axis; uprightover a mould 4 (Figure 1) Which has an accurately formed cavity 5 of desired curvature and depth. The envelope is clamped to a suitable support (not shown) which permits the envelope to be lowered on to the mould and be raised there! I from as desired and also to be secured firmly in either position. The interior of the envelope is connected to a supply of compressed air or other suitable gas, for example nitrogen or carbon dioX-- ide, by means of tube 8 so that the said gascan be blown into the interior of the envelope so as to raise the pressure therein when desired. The mouldis provided with an annular sleeve 6 wh ch for convenience is made separately from the mould i but capable of being screwed or otherwise secured thereto by means not shown, and which is, of such a diameter as to fit closely around the bulb .2 of the envelope when the latter is lowered on to the mould.

With the envelope secured in raised position as shown, a heater which may consist of a number of radially disposed gas burners, is applied to the endwall l-until the said wall has been heated to softening temperature. At the same time the mould 4 is heated either by means of further gas burners, or in a furnace, to a temperature sufficient to avoid-chilling the heated wall I when it is subsequently lowered on to the mould, but insuflicient to cause oxidation or distortion of the surface of. theca ty 5. the end wa1 ...l of

then removed from the mould.

The sleeve 6 is employed to prevent any in- I crease in the diameter of the envelope near the end wall I, since a portion of the bulb 2 adjacent the end wall inevitably becomes heated during the softening of the end wall I and said heated portion would be liable to expand under the internal pressure if not restrained. However, the heating is localised as much as possible to the immediate vicinity of the end wall l by a suitable disposition of the heating means so that the sleeve 6 need not extend over the whole length of the bulb 2.

The mould l and the sleeve 6 may be made from an iron alloy, such as the alloys known as Cronite and Meehanite, capable of withstanding high temperatures without appreciable distortion or scaling.

The method described can be applied with advantage to the manufacture of envelopes for cathode ray tubes which are provided with accurately formed internal protrusions extendin towards the axis of the envelope whereby the oathode ray gun can be accurately and positively aligned in the envelope, as described for example in British patent specifications Nos. 507,840 and 575,027, since it is possible to shape the end wall I of the tube accurately with reference to said protrusions. This may be done as illustrated in Figure 2 by mounting the envelope (here shown in longitudinal section) on a hollow mandrel 9 which is positively maintained in accurate coaxial relationship with the envelope by the protrusions [0 on the neck 3 which engage the mandrel, the mandrel 9 being itself clamped by a clamp [2 to a support which allows the mandrel to be positively and accurately aligned with the mould 4 and, with the envelope, to be raised and lowered as desired. The projecting end of the mandrel 9 is in this case connected to the compressed air or gas supply by the tube 8, so that during the moulding operation the air or gas is admitted to the bulb 2 through the interior of the mandrel. The mandrel is fitted with a rubber gasket H or other means which, when the envelope is lowered on to the mould 4, is pressed by the aforesaid support against the open end of the neck 3 so as to form a gas-tight seal. In Figure 2 the end wall l is shown after the moulding operation has been completed.

Asan alternative to employing a. hollow mandrel, external locating surfaces l4 may be formed on the neck 3 in accurate coaxial relationship with the internal protrusions 10, the envelope in this case being positioned in the support by clamping it at said locating surfaces by the clamp l2.

As illustrated the end wall I is shown moulded to a spherical curvature, but it will be understood that the surface may be made to conform to other shapes.

What we claim is:

1. A method of manufacturing an envelope having a glass window of predetermined curvature fused to a surroundin portion of said envelope, comprising the steps of polishing the surfaces of a glass portion to form said window, fusing said polished portion to said surrounding portion-of the envelope, and subsequently shaping said polished portion to said predetermined curvature.

2. A method of manufacturing an envelope having a glass window of predetermined curvature fused to a surrounding portion of said envelope, comprising the steps of fusing a glass member to said surrounding portion of the envelope to form said window, and subsequently moulding said member to said predetermined curvature.

3. A method of manufacturing an envelope of a cathode ray tube for use in a television receiver of the projection type and comprising a Wall of predetermined curvature forming the window of said envelope, said method comprising the steps of polishing a glass portion to form said window, fusing said glass portion to said surrounding portion of the envelope, and subsequently shaping said polished glass portion to the predetermined curvature.

4. A method of manufacturing an envelope of a cathode ray tube for use in a television receiver of the projection type and comprising a wall of predetermined curvature forming the window of said envelope, said method comprising the steps of using a glass member to said surrounding portion of the envelope to form said window,-and subsequently moulding said member to the pre-v determined curvature.

5. A method of manufacturing the envelope of a cathode ray tube, the end wall of which forms the optical window of said envelope, said method comprising the steps of polishing the surfaces of a flat glass disc, fusing said disc to the end of said envelope, and subsequently moulding said disc to curved formation.

6. A method of providing the envelope of a cathode ray tube with a curved optical window forming the end wall of said envelope, said envelope having locatingsurfaces accurately formed in relation to the axis of said envelope, said method comprising the steps of fusing a flat glass disc to the end of the tubular part of said envelope to close said end, locating said envelope on a support by means of said locating surfaces, locating a mould having a curved surface by means of said support so that the centre of curvature of said mould surface lies on the axis of said envelope, heating said glass disc to softening temperature, applying said envelope to said mould to mould the exterior surface of said glass disc uniformly into contact with said curved mould surface.

'7. A method of providing the envelope of va cathode ray tube with a curved optical window forming the end wall of said envelope, said envelope having locating surfaces accurately formed in relation to the axis of said envelope, said method comprising the steps of polishing the surface of a glass disc to render said surface optically fiat, fusing said glass disc to the end of said envelope to close said end, locating said envelope on a support by means of said locating surfaces, locating a mould having a concavely curved surface by means of a support with the centre of curvature of said mould surface lying on the axis of said envelope, heating said glass disc to softening temperature, applying the envelope to said mould and blowing gas into said envelope to mould the exterior surface of said glass disc uniformly into contactwith the concavely curved mould surface.

8. A method of manufacturing an envelope having a glass window of predetermined curvature fused to a surrounding portion of said envelope, comprising the steps of fusing a glass portion to said surrounding portion of the envelope to form said window, applying said window to a mould having a surface curved to said predetermined curvature, and blowing gas into said envelope to mould said window to the curvature of said mould surface.

9. A method of manufacturing an envelope comprising a glass window of predetermined curvature fused to a surrounding portion of the envelope, comprising the steps of fusing a glass member having optically flat surfaces to said surrounding portion of the envelope to form said window, applying the window to a mould having a curved surface of said predetermined curvature, and blowing gas into the interior of the envelope to mould the exterior surface of said glass member uniformly into contact with said curved mould surface.

20 Number 10. A method of providing the envelope of a.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Pedersen et al Nov. 6, 1934 Cary et a1. Apr. 11, 1944 

